In recent years, studies on the optically compensated birefringence (OCB) cell that is to be used as a liquid crystal cell instead of a twisted nematic (TN) cell have been quickly increased. In the OCB mode liquid crystal device, the liquid crystal molecules therein are in splay state at the initial state. However, when a voltage is applied to the OCB mode liquid crystal device, the liquid crystal molecules therein will transit from the splay state to the bend state, and it is required to spend some time for the transition from the splay state to the bend state. In the bend state, the top and bottom liquid crystal molecules are always oriented symmetrically, and thus to compensate the birefringence of liquid crystal molecules so as to obtain the uniform viewing angle characteristic at all directions is more easily than that obtained with the orientation division method, and a high-speed response characteristic that is one order faster than that for the conventional TN cells may also be obtained accordingly.
FIGS. 1A and 1B respectively illustrate the liquid crystal molecules in splay state and bend state in the OCB mode liquid crystal display device. As shown in FIG. 1A, in splay state, the liquid crystal molecules 104 are uniformly splayed between the glass substrates 100 and 102. However, when a voltage is applied to the glass substrates 100 and 102, the liquid crystal molecules 104 will be in bend state, as shown in FIG. 1B. In which, the transition time of the liquid crystal molecules 104 from the splay state to the bend state is one of the determinants for the OCB mode liquid crystal display device due to the fact that all the electro-optical properties of the OCB mode liquid crystal display device are operated when the liquid crystal molecules therein are in bend state.
However, some pixel structures have been disclosed, such as those disclosed in U.S. Pat. Nos. 6,115,087, 6,226,058, 6,661,491 and U.S. Pat. No. 6,597,424, but, some of them are not suitable for OCB mode liquid crystal display devices and there still exist some demerits in the disclosed pixel structures. In addition, the conventional pixel structures usually have the demerits, for example, a space exists between the pixel electrode and the gate electrode, and the common electrode must be introduced and overlapped with the pixel electrode for a certain area so as to form a storage capacitor. However, the above two demerits will result in a small aperture and cause the conventional pixel structures incompatible with the three-level gate driving.
In addition, although some driving methods for a liquid crystal device have been disclosed, such as that Takayuki Konno et al., (U.S. Pat. No. 6,873,377) and Katsuji Hattori et al., (U.S. Pat. No. 6,671,009) have disclosed a driving method for an OCB mode liquid crystal display and Hajime Nakamura et al., (U.S. Pat. No. 6,005,646) have disclosed another driving method for a thin film transistor liquid crystal display (TFT/LCD), there still exist some defects in the disclosed driving methods. For example, the driving method proposed by Katsuji Hattori et al. has a complicated signal input procedure and the applied system design always needs an alignment transition driving circuit, a switching control circuit and a switching circuit. In other words, the cost for the driving method of Katsuji Hattori et al. is always high and the relevant driving method is not so practical, especially for the trend of compactness. In addition, since the potential difference between the signal electrode and the common electrode is morn than 10 volts and that between the gate electrode and the signal electrode is also more than 10 volts in the driving method proposed by Hajime Nakamura, there might exist some problems about the poor uniformity and the slow transition time in driving method of the prior arts.
As above, since all the electro-optical properties of the OCB mode liquid crystal display device are operated only when the liquid crystal molecules therein are in bend state, the liquid crystal molecules in the OCB mode liquid crystal display devices need to be transformed from the splay state (non-display state) into the bend state (display state) before being used and there still exist some demerits in the conventional pixel structures and driving methods, new driving methods with shorter transition time and new pixel structures contributive to shorten the transition time for activating OCB mode liquid crystal display device are desired.